1. Field of the Invention
The present invention relates generally to a fluid supply for an occupant restraint system of the type having an expandable confinement which is expanded by the fluid supply to restrain movement of an occupant of a vehicle during a collision.
2. Description of the Prior Art
The expandable confinement has a collapsed inoperative condition for storage in a steering wheel, dashboard, or other location within a vehicle forward of a normal occupant position. Upon the occurrence of a collision of the vehicle, expansion of the confinement is generally effected by a fluid supply in the form of a pressure vessel defining a single chamber which contains stored pressurized gas. The stored gas is released from the chamber by rupturing a portion of the pressure vessel which communicates with a gas directing means, such as a diffuser, communicating with the interior of the confinement.
With such an occupant restraint system, the complete expansion of the confinement must occur within an extremely short period of time, e.g., less than one hundred milliseconds, after the initial impact in order to effectively restrain the occupant. The portion that is ruptured in the single chamber fluid supply is fixed in size and configuration. In order to complete expansion of the confinement within the desired time period, the ruptured portion is of a size which results in the mass flow rate of gas from the chamber reaching a maximum value almost immediately after the rupturing occurs. After reaching the maximum value, the mass flow rate of gas gradually decreases during the continued expansion of the confinement. Although such a fluid supply performs satisfactorily in most instances, it would be desirable to be able to control the mass flow rate of gas from the fluid supply from the time gas begins to enter the confinement until the time the confinement is fully expanded.